Chemically bonded magnesite brick



Nov. 18,' 1969 BQ DAVIES ETAL CHEMICALLY BONDED MAGNESITE BRICK 2 Sheets-Shee Filed Aug. 1s, 196s v N95 hkkvl QQ m m R n W V 0 WMNW DM 4 N m H.

United States Patent O U.S. Cl. 106-58 6 Claims ABSTRACT OF THE DISCLOSURE Chemically bonded magnesite brick having a soluble sodium phosphate binder and extremely high tensile strength as a result of the formation in service of a calcium sodium silicophosphate bond.

RELATED CASES This case is a continuation-impart of application Ser. No. 607,983, filed Jan. 9, 1967, entitled Chemically Bonded Magnesite Brick. The latter case has been abandoned.

BACKGROUND Magnesite brick are manufactured substantially from dead burned magnesia which, in refractories art, is termed magnesite. Chemically bonded brick are those which are bonded by a chemical'binder Without the use of a burning process. Ceramically bonded brick are those which are bonded by sintering which takes place during a burning process.

This invention is related to the above-mentioned copending application. That application discloses unburned or chemically bonded brick having a calcium silicophosphate bond. This invention is directed to unburned, chemically-bonded magnesite brick having a soluble sodium phosphate binder, which brick may be used (among other places) in the walls of steelmaking open hearth furnaces, in induction furnaces used for melting ferrous and nonferrous metals, and in glass tank regenerator walls and checker settings.

Some recent work regarding testing of phosphates in magnesite brick was reported in Improved Chemical Bonds For Basic Refractories, by R. W. Limes and R. O. Russell, a paper presented at the American Ceramic Society Annual Meeting, Philadelphia, Pa., May 3, 1965. In that work, it was found that excellent hot tensile strength at 2300 F. could be obtained by bonding magnesites containing dicalcium silicate with long-chain sodium phosphate glasses. It has now been found, however, that these brick had almost no transverse strength when tested at 26 00 F.

Accordingly, it is an object of this invention to provide chemically bonded magnesite brick with improved tensile strength (as measured by transverse loading). It is another object to provide a magnesite brick With a sodium phosphate binder that has a modulus of rupture at 2600 F. in excess of 500 p.s.i.

BRIEF DESCRIPTION This invention is predicated upon the discovery that soluble sodium phosphate binders can impart high-temperature strength as Well as room temperature strength to chemically bonded magnesite brick when the Cao i P305 weight ratio of the brick is suiciently close to the dicalcium silicate-tricalcium phosphate join on the ICC CaO'SIOg-P205 ternary diagram.

Preferably, brick made according to this invention are formed from a batch consisting essentially of size-graded dead burned magnesite grain and a soluble sodium phosphate binder. The brick analyze about 2 to 13 CaO-l-Si02, and Ihave a Ca0zSiO2 weight ratio between about 2:1 and 12:1. The sodium phosphate binder should yield at least about 0.5 P205. The Ca0:SiO2:P205 weight ratio should fall within the approximate area A-B-C-D-E on FIG. 1. The magnesite grain should contain no more than about 1.3% and, preferably, less than 0.5% uncombined or free CaO determined by calculation.

BRIEF DESCRIPTION 0F THE DRAWINGS FIG. 1 is a ternary diagram which graphically shows the Ca0:Si02:P205 weight ratios which are suitable for brick manufacture according to the teachings of this invention.

FIG. 2 contains X-ray diffraction patterns of one of the examples hereinafter discussed.

DETAILED DESCRIPTION Further features and other objects and advantages of this invention will become clear to those skilled in the art by a careful study of the following detailed description. In the detailed description, all sizings are reported by Tyler screen series; all percentages and parts are by weight; chemical analyses were obtained by spectrographic analysis with control by wet chemical analysis, and are reported as oxides in accordance with the present practice of the refractories industry.

The precision and accuracy of analytical spectrochemical data, particularly for CaO, Si02 and P205, is about 15.0 percent of the total weight percentage of the oxide reported, as determined by the method described by the American Society for Testing and Materials in Methods for Emission Spectrochemical Analysis (1964). For example, the precision and accuracy for a P205 determination reported to be 1.0 percent would be 10.5 percent, indicating the P205 contained in the sample analyzed by spectrochemical techniques to be between 0.95 and 1.05 Weight percent. The precision and accuracy of CaO, Si02 and P205 ratios, which are calculated by normalizing weight percentage spectrochemical data for these oxides to 100, closely approximates the 15.0 percent precision and accuracy of the analytical spectrochemical data. Consequently, the precision and accuracy for a normalized CaO ratio calculated to lbe 60 is 13.0, indicating the CaO ratio to be between 57 and 63. This is the reason that compositions of the invention are stated to be sufficiently close to the dicalcium silicate-tricalcium phosphate join or in the approximate area A-B-C-D-E.

The detailed discussion is made with reference to FIG. 1, which is a ternary diagram on which the relative proportions of CaO, Si02, and P205 of the exemplary mixes are plotted. Proportions were calculated from the chemical analysis without reference to MgO, or other oxides, the major components of the refractory Iwhich, of course, have no iniluence on proportions of the CaO, Si02, and

FIG. 1 utilizes the principles which characterize all such three-component diagrams. In FIG. l, each side of an equilateral triangle was divided into parts, each fth part being intersected by a line parallel to each of the other two sides. A point at each corner represents 100 parts, by weight, of one of the three components. In FIG. 1, the apex represents 100 parts of Si02; the lower lefthand corner represents 100 parts of CaO; and the lower right-hand corner represents 100 parts of P205. In any ternary diagram, the three sides are binary systems. For

example, a point on the base line of FIG. 1 is composed exclusively of the lower corner components CaO and P205. The relative distance of a point from each of the three corners may be expressed in parts; and it, thus, may rep- 4 weak at elevated temperatures. As a matter of fact, prior art burned brick had strengths at 2600 F. of less than about 500 p.s.i. until our invention disclosed, in the parent application, Ser. No. 607,983.

resent a proportion composition of a ternary mixture. All 5 The preferred composition and best known mode now points on a line through one of the corners must have known for the practice of the present invention is emthe same ratio of the components of the other two corners. bodied in Example III.

This invention is based upon the discovery that certain Example V was prepared from a grain that contained calcium sodium silicophosphates provide a refractory 1.29% uncombined lime calculated by the following bond for magnesite brick. Briefly, we have found that formula: those brick in which the Ca0:Si02:P205 weight ratio falls near the dicalcium silicate-tricalcium phosphate join Free CaOzC-(ZSS +1'01A+7F+1'17P on the diagram have unexpectedly high hot tensile strength. where,

By dicalcium silicate-tricalcium phosphate join, we mean the line on the diagram joining the compound of CaO and l5 Szpercentage SOZ;

S102 having a molar ratio of 2:1 and the compound of Czpel-Centage Cao;

CaO and P205 hav'ing a molar. ratio of 3:1. Except where A=percentage A1203;

mola;i ratio is specified, the oxide ratios referred to 1n this Fzperntage F6203.; and speci catlon are by weight.. P=.percentage P205 in the grain.

A series of brick according to this invention (Examples l I to VI) were prepared from batches as shown in Table I. This calculation assumes that the lime will combine to The various dead burned magnesites were prepared by form tricalcium silicate, tetracalcium phosphate, dicalcium making small additions of silica, lime hydrate, apatite, or ferrite, and dicalcium aluminate. The mix of Example V, phosphoric acid to caustic magnesite, briquetting the mixwhen being tempered, became very warm and tended to tures and dead burning the briquettes at temperatures in dry out. Hence, 1.301% free lime is considered the largest excess of 3000u F. No phosphate materials were added amount of free lime that can be tolerated according to to the grains used in the preparation of Examples II and this invention. Preferably, the free lime should be less V. The dead burned magnesite grains were sized and than 0.5%. In order that the free lime in the starting grain graded to form pressable brickmaking batches. Suitable be minimized, it is necessary when the CaOzSi02 ratio size gradings are shown in Table I. The size lgraded dead is high to add P205 to the grain. Notice Example VI was burned magnesites were combined with a small quantity manufactured from a grain containing 6.60% CaO and of sodium phosphate glass binder shown in the table, and had a Ca0zSi02 ratio of 10.8: 1. However, it did not heat tempered with the small addition of Water also shown in up on tempering as there was no uncombined CaO as calthe table. The tempered batches were pressed into brick culated by the formula set forth above. at about 8000 p.s.i. The brick were dried at about 250 F. 35 It had been our experience that a magnesite grain confor about 10 hours and, thereafter, tested for bulk density taining more than 0.2% free C30 would heat up when and modulus of rupture at room temperature, 2300 F., tempering with conventional binders and crack when being and 2600 F. The results of the testing are also shown in dried. The sodium phosphate binder, however, is excep- Table I. The CaO:SiO2:P205 ratios of the exemplary brick tional in that it permits the presence of a larger amount of after testing at 2600 F. are plotted on FIG. 1. 40 free lime.

TABLE I Example I II III IV V VI Batch, percent:

agnesite:

-4-1-10 mesh 32 32 32 20 32 32 10+2s mesh 33 32 33 34 32 33 Banmi119d11nes(55%-325mesh). 33 33.25 33 34 33.25 33 Sodium Phosphate Glass 2 2. 75 2 2 2.75 2 Water Added 3 3 3 3 3 3 3.7 1.5 1.4 0.3 0.74 0.63 0. 61 0.49 0.45 0. 3s 0.41 0.41 0.22 0.25 0.20 0. 20 0.21 0.26 3.20 4.5 5.10 3.71 3.9 6.60 (MgO) The Remainder Phosphorus Oxide (P2O5) 0.51 0.1 0. 55 0.70 0.1 4.0 Boron oxide (B203) 0.095 0.12 0.11 0.11 0.12 0.11 Chemical Analysis of Brick After Testing at 2,600 F., percent:

silica (S102) 3.8 1.5 1.3 0.8 0.65 0.6 Aiumina (111203).. 0. 6i 0.49 0.45 0.33 0.41 0.41 Iron Oxide (F6203) 0.27 0.25 0.25 0. 20 0. 25 0.29 Lime (cao) 8.7 4.6 4.4 3.71 3.90 6.5 Magnesia (MgO) The Remainder Phnsphorous 0166603205). 1.40 1.40 1.70 1.90 1.5 4.6 Boron 01011603203) 0.075 0. 085 0.075 0.09 0.085 0.075 Soda (N310 0.56 0.66 0. 57 0.61 0.63 0.60 0304-3102 12.5 6.1 5.7 4.5 4.55 7.1 060:3102 ratio 2.3:1 306:1 3 411 4.6;1 6.0;1 10.3;1 Buik Density, pcf 180 181 180 130 182 175 Modulus of Rupture, p.

Table I establishes that brick made according to the teachings of the present invention have tensile strength at 2600" F. as tested by the -modulus of rupture over 500 p.s.i. This is considered indeed surprising because chem- In order to demonstrate the necessity for CaO Si02 P205 ratio to be close to the dicalcium silicate-tricalcium phos ically bonded brick (uriburned) are known to be very phate join, Examples VII, VIII, and IX were prepared in 5 the same manner as Examples I through VI. Notice that they fell just outside of the area A-B-CD-E on FIG. 1. Example X was prepared in the same manner as the other examples, but according to the present invention.

TABLE II Example VII VIII IX X Batch, percent:

Magnesite:

-4-1-10 mesh 30 30 32 29. 5 -10-1-28 mesh 34 34 33 34. 5 Ball milled fines (55%-325 mesh) 34 33 34. 5 Sodium Phosphate Glass 2 2 2 1. 38 Water Added 3 3 3 3 Chemical Analysis of Brick After Testing at 2,600 F., percent:

Silica (S102) 1. 1 1. 4 1. 1 0. 70 Alumina (A1503) 0. 50 0. 55 0. 44 0. 36 Iron Oxide (FezOa) 0. 31 0.31 0 24 0.27 Lime (CaO) 3. 80 3.6 5.0 2. 25 Magnesia (MgO) The Remainder Phosphorous Oxide (P205 1.9 1. 9 1. 4 0. 94 Boron Oxide (B203) 0. 07 0. 08 0.1 0.02 Soda (Nago) 0. 65 0. 63 0. 60 0. 43 CaO-l-SiOz 4.9 5.0 6.6 2.95 CaO:SiOiratio 3.5:1 2.6:1 4. 55:1 3.2:1 Bulk Density, pcf 179 180 177 182 Modulus o Rupture, p 420 1,210 610 1, iso 460 1, 590

Table II establishes that the area A-B-C-D-E on FIG. 1 is critical. All mixes except Example X had relatively low modulus of rupture at 2600 F.

It should be understood it is not necessary for mixes according to this invention to have CaO:Si02:P2O5 ratios precisely on the dicalcium silicate-tricalcium phosphate join. The suitable ratios are within the approximate area A-BACDE on FIG. 1. It has been found that mixes having CaO:SiO2:P2O5 ratios within this area are sufliciently close -to the dicalcium silicate-tricalcium phosphate join to have strength in excess of 500 p.s.i. in the modulus of rupture test at 2600 F. Line D-E has a CaOzSiO2 ratio of 12:1; line F-G a CaO:SiO2 ratio of 6:1; and line BAC has a CaO1Si02 ratio of 2:1. It has been found thiat mixes having CaOzSiO2 ratios between 2:1 and 6:1 are more easily manufactured. Hence, it is preferable that the brick made according to this invention have CaO1Si02IP2O5 ratios falling within the approximate area A-B-C-F-G on FIG. 1.

While it is not necessary that the dead burned magnesite grain contain any P205, it is desirable that the grain contain at least 0.2% P205, preferably between about 0.2 and 1%. It has been found that brick made from grain containing iat least 0.2% P205 is easier to manufacture and consistently have superior properties. This is especially true for magnesite grains having a high CazSi02 ratio.

While it is preferred according to this invention to manufacture brick by combining dead burned magnesite grain |and a soluble sodium phosphate binder, it is possible to adjust the' 'Ca0:Si02:P205 ratio by making additions of silica and apatite or other CaO, Si02, and P205 yielding materials to the brick batch.

To obtain a better understanding of our invention, X-ray difnaction studies of Example IV were carried out at various temperatures after various heat treatments. The X-ray diffraction patterns are given in FIG. 2. The grain from which brick in Example IV were prepared contained nagelschmidtite (a calcium silicophosphate) as the predominant mineral component other than periclase (see pattern IVa on FIG. 2). The grain had a CaO:Si02:P2O5 molar ratio of about 101221. A calcium sodium silicophosphate phase was developed in the brick after bonding with sodium phosphate glass and heating to 2300 and 2600 F. (patterns IVb and IVc). The brick had a CaO2Na201Si022P205 molar ratio of about :0.7:1:1. High-temperature X-ray diffraction analysis in the temperature range up to 2600 F. showed no inversion of the calcium sodium silicophosphate structure. The structure of the high-temperature form at 2600 F. (pattern IVd) and at room temperature are concordant. Finally, it was found that the structure of the calcium sodium silicophosphate phase became better ordered after extended periods at elevated temperatures (pattern IVe). While we do not completely understand the scientific basis for our invention, we believe soluble sodium phosphate imparts high-temperature strength to chemically bonded magnesite brick by the development in service of a calcium sodium silicophosphate bond. Excellent hot strength at 2600 F. is attained in t-he calcium sodium silicophosphate compositional range approximating the 2CaO-Si02-3CaO-P205 join of the 2CaOSi02 3Ca0-P2O5-Na20 plane in the system compositional points mark the areas of optimum hightemperature strength. The calcium sodium silicophosphate solid solution is developed in a solid state reaction between sodium phosphate and various calcium silicates or calcium silicophosphates at relatively low temperatures (below 2300 F.) aided, apparently, by the reactionaccelerating effect of the sodium cation. The refractoriness of the system is not affected detrimentally by the limited presence of sodium. Sodium enters the calcium silicophosphate structure filling vacant calcium positions in the lattice which are unoccupied because of the difference in valence between SiO4 and PO.,= groups. Substances, particularly solid solutions, with unoccupied cation positions are not unusual. In effect, the sodium ions are isolated Ild not available for reaction with other cornponents to form low melting compounds. The structure of the calcium sodium silicophosphate solid solution is analogous to the high-temperature form of the calcium silicophosphate solid solution series suggesting that sodium effectively stabilizes the calcium silicophosphate structure in its high-temperature form. Strength variations at elevated temperatures, attributable to structural inversions, are consequently eliminated.

RAW MATERIALS AND TEST PROCEDURES As a soluble sodium phosphate binder, we prefer a sodium phosphate glass which is molecularly dehydrated and polymerized. These have an Na20-P205 ratio generally ranging from 1.1: to 1.8:1. These glasses are highly soluble, but retain their molecular structure well in such solutions. Commercial metaphosphate glasses (Na2OzP2O5 ratio is 1:1) include Glass H and Glass A, proprietary products of the F.M.C. Corporation, and Calgon, a proprietary product of the Calgon `Corporation. Quadrophos is a proprietary product of the Rumford Chemical `Corporation and is a suitable sodium phosphate glass which has an Na2OrP2O5 ratio of 1.5: 1.

The bulk density of the sample was determined by ASTM methods 'C134-41, Manual of ASTM Standards on Refractory Materials, 9th edition, 1963, pages 154 et seq. Modulus of rupture at room temperature was determined by ASTM Methods C133-55, pages 145 et seq. of the same manual; modulus of rupture at room temperature, except this test was performed in an electricallyheated furnace.

PHASE STUDIES Standard X-ray powder diiraction procedures were followed in the qualitative determination of the phase composition of the refractory test specimens.

A General Electric XRD-5 X-ray Ditfractometer unit equipped with spectrogoniometer, gas-flow proportional counter, and potentiometric strip-chart recorder was used. Powder mounts were scanned in the angular range 5 to 70 20 using Ni-filtered Cu K2 radiation. Instrument settings were: tube voltage 50 kv.; tube current 13.5-15.5 ma.; input discriminator 2.5 v.; beam slit 3; receiving slit 0.2; time constant 2 seconds; recorder range 2000 counts per second; and scanning speed 2 20 per minute.

Interplanar (d) spacings and relative intensities of reections were determined from `diffraction patterns by calculation using tables of interplanar spacings as a function of 20 and by visual estimation with a calibrated scale. Identification of the diiracting phases was effected following a standardized procedure in which d values and relative intensities were compared with published diffraction data and reference patterns. The primary reference source for powder diffraction ydata was the Powder Diifraction File, published by the American Society For Testing Materials (1964). The Numerical (Hanawalt), Alphabetical (Davey), and Fink indexes to the Powder Diffraction File were used. Additional diifraction data was obtained from published scientific papers.

Having thus described the invention in detail and with sufcient particularity as to enable those skilled in the art to practice it, what is `desired to have protected by letters patent is set lforth in the following claims:

We claim:

1. Chemically bonded magnesite brick having a soluble sodium phosphate binder, said brick having a CaO:SiO2:P2O5 ratio suiciently close to the dicalcium silicate-tricalcium phosphate join on the CaOSiO2P2O5 ternary diagram to form a calcium sodium silicophosphate bond when heated, the brick having a modulus of rupture at 2600 F. of at least 500 p.s.i.

2. Chemically bonded magnesite brick according to claim 1, in which the brick is formed from a batch consisting essentially of dead burned magnesite grain containing less than about 1.3% free lime and a sodium phosphate glass binder yielding at least 0.5% P205, said brick analyzing about 2 to 13% CaO-i-SiOz, said brick having a CaOzSiO2 weight ratio between about 2:1 and 12:1, said brick having a CaO:SiO2:P2O5 weight ratio falling within the area A-B-C-D-E on FIG. 1.

3. Brick made according to claim 2 having a CaO:SiO2:P2O5

ratio falling within the area A-B-C-G-F on FIG. l.

4. Brick made according to claim 2 in which the magnisite grain contains between 0.2 and 1% P205.

5. Brick according to claim 2 in which the magnetic grain contains less than about 0.5% free lime.

6. Brick according to claim 2 in which the batch comprises lime, silica, and phosphate-yielding materials.

References Cited UNITED STATES PATENTS 

